METHOD FOR MEASURING MASS FLOWS IN FLOW DUCTS

Abstract: Method for measuring mass flows in a dispersion flow. In the method, the concentration of the substance under measurement in the dispersion flow and the velocity of flow of said substance in the flow duct are measured. The velocity of flow is measured by a marking procedure by altering the absorption properties of the dispersion flow. The volume flow of the dispersion is determined on the basis of the velocity of flow and the cross-sectional area of the flow duct and the mass flows are determined on the basis of the concentration and the volume flow.

Description: METHOD FOR MEASURING MASS FLOWS IN FLOW DUCTS The present invention relates to a method for measuring mass flows in a dispersion flow in a flow duct. In this application, 'dispersion flow' refers to material flows in which gaseous, liquid or solid substances are mixed as disperse phases in a gaseous, liquid or solid dispersion medium. 'Flow' means the flow of a dispersion in an open or closed flow duct. Dispersion measurements generally practised include e.g. the measurement of the solids content and mass flow of a gas containing solids and the measure¬ ment of the solids content [and] mass flow of a liquid containing solids. A practical example of such measu¬ rement is the measurement of emissions in combustion gases. Among important but as yet unrealized measuring methods are the mass flow measurement of coal dust fed into the burners of coal boilers and the measurement of drops in exhaust gases in so-called' wet desulphuri- zation procedures and in general the measurement of drops in gases after scrubbers. Currently used mass flow measurements have several drawbacks. The concentration of the dispersion is measured only locally in the flow and also the dis¬ persion flow rate is measured only locally in the flow, resulting in inaccurate and variable measurement results. Because of the erosion and corrosion problems caused by the properties of a dispersion, it has not been possible with current detectors and methods to create the measuring conditions required for a theore¬ tically correct measuring arrangement. The object of the present invention is to eliminate the drawbacks referred to above. A specific object of the invention is to produce a new measuring method that allows the mass flow in dispersion flows to be defined with maximal accuracy. As for the features characteristic of the in¬ vention, reference is made to the claims. In the method of the invention, to measure the mass flows in a dispersion flow, the concentration of a given substance in the dispersion flow as well as the velocity of flow of that substance in a flow duct are measured. The concentration measurement can be performed by a method known in itself, based e.g. on particle radiation or electromagnetic radiation. Ac¬ cording to the invention, the velocity of flow of the dispersion flow is measured by marking, i.e. by adding a suitable substance into the dispersion flow, so that the time taken for the marking substance to pass through a given distance, i.e. the velocity of move¬ ment of the substance in the flow can be measured. Based on the measured velocity of flow and the known cross-sectional area of the duct, the volume flow of the dispersion can be determined, whereupon the mass flow is determined on the basis of the concentration and volume flow. As the method of the invention can be used in a wide range of different dispersion flows for the me- asurement of gaseous, liquid and solid substances and because the concentration measurements can be perfor¬ med on the basis of particle radiation or electromag¬ netic radiation by the aid of absorption or permeati¬ on, the radiation energy to be used in the concentre- tion measurement is always selected on the basis of the properties of the substance to be measured. According to the invention, the marking can be can be performed by altering the absorption proper¬ ties of the dispersion medium or the substance under measurement, and this is preferably done by changing the concentration of the dispersion flow. The concent¬ ration can be reduced by a suitable addition of gas. e.g. air, or the concentration can be increased by ad¬ ding to the dispersion flow an amount of one or more of the substances flowing in it. The marking can also be effected using par- tide radiation, electromagnetic radiation or a sui¬ table chemical reaction. The marking is preferably performed simulta¬ neously over the whole cross-section of the flow duct, in other words, the cross-section of the flow duct is provided with a number of suitable nozzles placed on the same circle so that the gas, mass or substance is added substantially uniformly over the whole area of the cross-section. In addition, inhomogeneity of the flow is preferably . eliminated by using two or more transmit¬ ters and two or more receivers. It is also possible to use array detectors or elongated detectors. In this way, it is possible to produce suitable radiation wedges or bands across the flow duct that cover the flow duct cross-section to a sufficient degree. As compared to previously known technology, the method of the invention has the advantage that it allows accurate measurement of mass flows regardless of their physical and chemical properties, their cor- rosion properties. In the following, the invention is described by the aid of the attached drawings, in which Fig. 1 presents a diagram of a measuring arrangement according to the invention, Fig. 2 presents a diagram of an arrangement for con¬ centration measurement. Fig. 3 presents a diagram of another arrangement for concentration measurement, and Fig. 4 presents a diagram of a third arrangement for concentration measurement. The diagrammatic arrangement representing the measuring method of the invention as presented in Fig. 1 comprises a flow duct 1 in which the dispersion flow to be measured is flowing. The flow duct is pro¬ vided with a marking transmitter 5 with a flushing gas system 6 for passing a marking material inclusion 7 into the flow duct. After the marking transmitter 5 in the direction of flow there is a second transmitter 8 and on the opposite side of the flow duct a first receiver 9, and further down in the direction of flow a second receiver 10, placed close to the second transmitter. Moreover, at distance a from the marking transmitter 5 in the direction of flow and at distance b from the second transmitter 8 there is a third transmitter 11 and on the opposite side of the flow duct a third receiver 12. When the concentration of a desired substance or compound in the dispersion flow is to be measured, the second transmitter 8 transmits elementary par¬ ticles or electromagnetic radiation in a desired ener¬ gy or frequency band. The band is determined on the basis of the element, chemical compound or total mass to be defined. The concentration is determined by the aid of the absorption, permeation or scattering of the sub¬ stance under measurement or alternatively by the aid of the secondary particle or electromagnetic radiation induced by the marking transmitter 5 in the substance under measurement, on the basis of known or experimen¬ tally determined coefficients. Determination is per¬ formed either by the first receiver 9, which acts as an indicator of absorption, permeation or induced ra¬ diation, or by the second receiver 10, which acts as a detector of scattered and induced radiation. The velocity of flow of the dispersion is de¬ termined by measuring the time it takes for dispersion marked in a certain way to flow either through distan¬ ce a or through distance b. The marking is performed by using particle radiation, electromagnetic radiati- on, a chemical reaction or a diluting dispersion me¬ dium. When the marking is done using particle or electromagnetic radiation, the second transmitter 8 sends out through the dispersion a radiation which causes the substance under measurement to transmit particle or electromagnetic radiation induced by the first radiation. This induced radiation is detected by the third receiver 12 after the time it takes for the dispersion to flow through distance b. When the marking is done by means of a chemi¬ cal reaction or a diluting or thickening dispersion medium, a substance that reacts with the substance or compound under measurement or a diluting or thickening medium is injected by the marking transmitter 5 in the form of pulses through the flushing system 6 into the dispersion under measurement, forming a separate mar¬ king agent inclusion 7 in the dispersion. A chemical reaction between the marking agent and the substance or compound being measured now takes place on the boundary surfaces of the inclusion or inside the inclusion. The secondary radiation pro¬ duced by the chemical reaction is detected by the third receiver 12. The effect of the diluting or thickening me¬ dium on the reduced or increased concentration of the dispersion, respectively, is detected by the third transmitter 11 and the third receiver 12. If relative values are sufficient as measured values, the measure- ment can be carried out directly within distance a, i.e. during the passage of the inclusion from the mar¬ king transmitter 5 to the third receiver 12. If more accurate, absolute measured values are to be obtained, the measurement is performed within distance b, i.e. during the passage between the transmitter/receiver pairs 8,9 and 11,12. The velocity of the dispersion is obtained by dividing the distance a between the marking and measuring points or the distance b between the measuring points by the measured time of passage. After this, the volume flow of the dispersion is obtained as the product of the velocity of flow and the cross-section of the flow duct. The material or mass flow of the dispersion is obtained as the product of the material or mass concentration and the volume flow determined in the manner described above. Fig. 2 presents a preferred embodiment of the invention, in which the flow duct 1 is provided with four nozzles 6 placed at even distances on the same cross-section, enabling the marking agent inclusions 7 to be relatively evenly distributed over the whole area of the cross-section. Fig. 3 presents an embodiment in which the flow duct 1 is provided with two transmitters 2 and a shared receiver 3, allowing irregularities of flow to be eliminated in the concentration measurement. Anot¬ her corresponding solution is presented in Fig. 4, in which there is one transmitter 2 but two receivers 3 placed on the opposite side of the duct at a distance from each other. A still better elimination of irregularities of flow is achieved by the embodiment presented in Fig. 5, in which the flow duct 1 is provided with an elongated and curved detector consisting of a single continuous detector or an array detector 4, placed on the side of the duct opposite the transmitter 2. In this case, a substantially coherent radiation wedge 13 traverses the flow duct. If two such radiation wedges are used, as illustrated by Fig. 5, most of the cross- sectional area of the flow duct can be scanned by the concentration measurement. In the above, the invention has been descri- bed by way of example by the aid of the drawings at¬ tached, but different embodiments of the invention are possible within the inventive idea defined by the claims.

Claims: CLAIMS 1. Method for measuring mass flows in a dis¬ persion flow in a flow duct, characterized in that - the concentration of the substance under measurement in the dispersion flow and the velocity of flow of the substance under measurement in the flow duct (1) are measured, - the velocity of flow is measured by a marking proce- dure by measuring the time of passage of marked dis¬ persion through a given distance, - the volume flow of the dispersion is determined on the basis of the velocity of flow and the cross- sectional area of the flow duct, and - the mass flows are determined on the basis of the concentration and the volume flow. 2. Method according to claim 1, characterized in that the concentration measurement is implemented using particle radiation or electromagnetic radiation. 3. Method according to claim 2, characterized in that the radiation energy for the measurement of the concentration of the substance under measurement is selected on the basis of the properties of said substance. 4. Method according to any one of claims 1 - 3, characterized in that the marking is performed by altering the absorption properties of the dispersion flow. 5. Method according to claim 4, characterized in that the absorption properties are altered by alte¬ ring the concentration of the dispersion flow. 6. Method according to claim 5, characterized in that reduction of concentration is implemented by adding gas in a substantially pulse-like manner. 7. Method according to claim 6, characterized in that increase of concentration is implemented by adding to the dispersion flow an amount of one or more of the substances flowing in it, the addition being performed in a substantially pulse-like manner. 8. Method according to any one of claims 1 - 3, characterized in that the marking is performed using particle radiation or electromagnetic radiation. 9. Method according to any one of claims 1 - 3, characterized in that the marking is performed using a chemical reaction by adding to the dispersion a substance that reacts with the substance under mea¬ surement or with the dispersion medium. 10. Method according to any one of claims 6 - 9, characterized in that the addition of the substance is performed as a substantially smooth blow over the whole area of the cross-section of the flow duct (1). 11. Method according to any one of claims 1 - 10, characterized in that irregularities of flow in the concentration measurement are eliminated by using two or more transmitters (2) , two or more receivers (3) and/or an array detector or an elongated detector (4). 12. Method according to any one of claims 1 - 11, characterized in that the method is used for the measurement of emissions in combustion gases and other gases, for coal dust flow measurement and for the mea¬ surement of concentrations in liquid drops e.g. in de- sulphurization plants and scrubbers.

Inventors: HUOVILAINEN REINO, HUOVILAINEN, REINO
Applicants: HUOVILAINEN REINO, HUOVILAINEN, REINO
Application year: 1994
Main classification: G01F1
IPC codes: G01F1, G01N23, G01P5